[GHC] #7460: Double literals generated bad core

[GHC]

#7460: Double literals generated bad core
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    Reporter:  tibbe             |       Owner:                         
        Type:  bug               |      Status:  new                    
    Priority:  normal            |   Milestone:                         
   Component:  Compiler          |     Version:  7.4.2                  
    Keywords:                    |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
  Difficulty:  Unknown           |    Testcase:                         
   Blockedby:                    |    Blocking:                         
     Related:                    |  
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Comment(by tibbe):

 This is how the C standard defines integer to/from floating point
 conversions:

 6.3.1.4 Real floating and integer

 1 When a finite value of real floating type is converted to an integer type
 other than _Bool,
 the fractional part is discarded (i.e., the value is truncated toward
 zero). If the value of
 the integral part cannot be represented by the integer type, the behavior
 is undefined.
 61)

 2 When a value of integer type is converted to a real floating type, if the
 value being
 converted can be represented exactly in the new type, it is unchanged. If
 the value being
 converted is in the range of values that can be represented but cannot be
 represented
 exactly, the result is either the nearest higher or nearest lower
 representable value, chosen
 in an implementation-defined manner. If the value being converted is
 outside the range of
 values that can be represented, the behavior is undefined. Results of some
 implicit
 conversions may be represented in greater range and precision than that
 required by the
 new type (see 6.3.1.8 and 6.8.6.4).

 61) The remaindering operation performed when a value of integer type is
 converted to unsigned type
 need not be performed when a value of real floating type is converted to
 unsigned type. Thus, the
 range of portable real floating values is (−1, Utype_MAX+1).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7460#comment:11>
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